Help! Beginner Questions

I am planning to start working with my first laser in an etch a sketch laser plotter I've been building, which is intended to burn wood and if everything goes well various other materials as well. I have a few questions I've been unable to answer on my own, I hope you can help!

1. Will the standard 12x30mm Aixiz housing fit most laser diodes? Do I have to worry about sizing?
650nm 5mW laser module.3.2V to with lens 650 nm OEM - eBay (item 360293174546 end time Aug-30-10 14:31:00 PDT)

2. I am looking at the following two laser diodes.
Either this ultra-cheap 300mW IR diode:
808nm 300mW High Power Burning Laser Diode DIY Lab New - eBay (item 280543956960 end time Sep-02-10 14:19:31 PDT)
Or the more expensive 500mW IR diode found on this page(third from top):
Diodes : StoneTek Electronics, Your Laser Parts Store

Notice that on the stonetek page another 300mW IR diode is for sale for 11 dollars, as opposed to 1 dollar on ebay. Why is that? Will the ebay diode be a piece of junk? Can you give me some advice as to which diode I should choose, having wood and plastic engraving in mind?

3. For the laser diodes driver circuit I will follow the guide here:
Bulding a burning laser
In which the following schematic is supplied:
Driver.jpg (image)
I assume the given values for the capacitor, voltage source, etc. will vary from laser diode to laser diode, but the guide does not specify the laser diode this driver is catered to. How can I determine, for the diodes I've specified above for instance, how to tailor the driver to the particular diode? I've seen almost the exact driver schematic in a number of different places, but hardly ever is it specified for which diode the schematic is built. Is it not that important, or are most diodes rated the same?

Thank you

Hi again,
I've answered my first and third questions already. I would still appreciate advice about the 2nd question if anyone is willing, and I have one further question about the drive circuit.

Does the capacitance vary at all from diode to diode? Or will the 10uF 16V capacitor suffice for any and all?

i would stay away from ebay.

Are you wanting to just char the wood and turn it black or actually cut the wood?

Assuming you are just wanting to char the wood, I would recommend a 1w diode. They're not much more expensive, but will greatly improve burning speed and power.

Also, ebay is a fine place to buy diodes. Just be sure to check a user's feedback. I would recommend that you do a search on these forums. Never know what you might find!

And watch the shipping prices. And yes, you will usually get what you pay for.

Be sure to heatsink that sucker well!

Good luck with your project, and welcome to the forums!

Yes, just wood charring is what im after. After reading somebodies experience with a 300mW infrared diode, I bought two of those for a dollar each on ebay and will try my luck with them before spending anymore cash on a stronger diode. It seems he was quite successful with 300mW, although it may be a little slow.

Thanks!

Ive got everything I need to make the driving circuit for the 300mW infrared laser diode except the resistors, which I have yet to purchase.

It seems to me that the 1 Ohm resistor in the test load will be subject to 2.2V and 400mA, which is what Ive calculated should be ideal for the 300mW IR diode. So that works out to 1 Watt through this resistor.

I need a total of 3.125 Ohms in the actual driving circuit to set the maximum current at 400mA. For this one the reference voltage of the LM317 is 1.25 and with 400mA thats 0.5 Watts.

Is all that right? So should I buy a 1 Ohm 1 Watt resistor for the test load and for the other resistance get half Watt?

I just want to be sure before I buy them, Im not sure how much the Watt rating for resistors matters in practice.

Electronic geniuses will have to answer your specific questions above but I will ask what driver are you planning to build?

I do know that the Watt rating is just how much power the resistor can safely dissipate. It may well be able to cope with more but that's what it is gauranteed to take.

You haven't mentioned any goggles. Do you have these? You definitely need them!

I've seen a lot of people recently mentioning these $1, 300mW, 808nm diodes from Ebay and I honestly do not think that near IR diodes of this power are the best diodes to use for your very first laser. They are respectfully powerful diodes that emit light you can hardly see! My best advice would be at least to build a simple, visible wavelength laser before messing with high power IRs.

You can push an LOC, (from the LPC-815 sled), to maybe 250mW and get an idea just how bright this sort of output level really is, how much of a danger it poses, and learn how to handle high output lasers whilst being able to see the hazard. IR can give you a false sense of security. Learn to walk before you can run.

Have a look at the links in my sig for some useful hints and guides.

1W is far too much for your first ever build so don't go that way please.

BTW, don't forget to introduce yourself in the, "Welcome", section and tell us a little about yourself.

You're obviously using the search button and reading as you've answered some of your questions yourself. With that sort of start, you'll go far here! Check out the, "Rules and Stickies", if you haven't already that is!

M

Hi there, thank you for the welcome.
I am planning on building the driver detailed here:
Laser driver - It can be done
Ive determined thus far that ill need 6.2 volts in total. 2.2V for the diode, 3V for the LM317 and 1.2V as recommended on the above page for longer battery life.
Based on what ive read on the forums, it seems 400mA is an ideal maximum current through the IR diode of 300mW, so ill have roughly 3 Ohms of resistence for that. And for the test load, 3 diodes and 1 Ohm of resistance.

Oh yes, I am going to purchase IR goggles before I hook these puppies up. Ive got a few weeks before they arrive.

If the Watt rating is just how much the resistor can safely dissipate, perhaps it doesnt matter too much. If I buy a 1 Watt 1 Ohm resistor, and its only actually subject to 1/5 of a Watt, it will still be resisting 1 Ohm, right? As long as the actual power going through the resistor is below its rated Wattage I should be fine, is that the idea?

SenorFrog said:

Hi there, thank you for the welcome.
I am planning on building the driver detailed here:
Laser driver - It can be done
Ive determined thus far that ill need 6.2 volts in total. 2.2V for the diode, 3V for the LM317 and 1.2V as recommended on the above page for longer battery life.
Based on what ive read on the forums, it seems 400mA is an ideal maximum current through the IR diode of 300mW, so ill have roughly 3 Ohms of resistence for that. And for the test load, 3 diodes and 1 Ohm of resistance.

Oh yes, I am going to purchase IR goggles before I hook these puppies up. Ive got a few weeks before they arrive.

If the Watt rating is just how much the resistor can safely dissipate, perhaps it doesnt matter too much. If I buy a 1 Watt 1 Ohm resistor, and its only actually subject to 1/5 of a Watt, it will still be resisting 1 Ohm, right? As long as the actual power going through the resistor is below its rated Wattage I should be fine, is that the idea?

Click to expand...

Yes, that's the idea but if you're going to be building any other lasers then you'll need to replace it at some stage I would think.

Glad you're goggles are being sorted!

6.2V seems pretty high to run a 2.2V diode? It's not a problem as the drvier will just dissipate any extra power as heat. It's been a while since I used a DDL so I may be out of touch here.

M

"
Voltage needed by red LD 3v
Voltage needed by regulator to make it work 3v
Additional voltage to get long life between battery changes 1.2v.
Add that up and you get 7.2volts
"

from:
Laser driver - It can be done

And since an infra red laser diode requires approximately 2V, I followed the above process to get 6.2V in total. Is the above the best way to do it?

I acquired yesterday for free two rechargable Nickel Cadmium battery packs for a remote control car. On them it says 7.2V and 1400mAh. I also got the charger, so I would very much like to use these to power my laser, will that be a problem? Its 1V higher than what the website above says is ideal, but if the regulator will dissipate this extra volt into head it wont matter very much right? Is a rechargable Ni-Cd battery a suitable power source for this?

I havent yet charged them so im not sure how much they will put out when fully charged. They could be quite old.

Your ideas sound pretty sensible so far.

(I am don't think the LM317 require more than the 1,25V across it's current setting resistor. So it could likely be run with just 4,5-5V, plus voltage drop on the battery.)

7,2V will be fine for your purpose, as long as you ensure sufficient heatsinking of the LM317.
It has a nice hole in it for bolting it onto a metal plate.